Shado

Shado, a ghost boss, is available only in the Halloween World event. It has no stages and only uses its hands to attack. The boss drops 5 gems and lots of coins, but they are not directly given to the player(s) who killed Shado. They are dropped on the ground where anybody can take them, so you must get them before anyone else does. This boss has no chest and takes 1 hour to respawn.

Image Credit: Draco O